Debt (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Long-Term Debt, by Current and Noncurrent, and Short-Term Debt
Short Term and Long Term Debt	$ 473,675
Less: current portion	(28,817)	(28,300)
Long-Term Debt
Long-term debt	444,858	476,715
US Dollar Amounts [Member]
Long-Term Debt, by Current and Noncurrent, and Short-Term Debt
Short Term and Long Term Debt	428,000
Less: current portion	0
Long-Term Debt
Long-term debt	428,000
Other Principal Trading Currencies [Member]
Long-Term Debt, by Current and Noncurrent, and Short-Term Debt
Short Term and Long Term Debt	45,675
Less: current portion	(28,817)
Long-Term Debt
Long-term debt	16,858
6.30% Senior Notes [Member]
Long-Term Debt, by Current and Noncurrent, and Short-Term Debt
Short Term and Long Term Debt	100,000
6.30% Senior Notes [Member] | US Dollar Amounts [Member]
Long-Term Debt, by Current and Noncurrent, and Short-Term Debt
Short Term and Long Term Debt	100,000
6.30% Senior Notes [Member] | Other Principal Trading Currencies [Member]
Long-Term Debt, by Current and Noncurrent, and Short-Term Debt
Short Term and Long Term Debt	0
Credit facility [Member]
Long-Term Debt, by Current and Noncurrent, and Short-Term Debt
Short Term and Long Term Debt	344,858
Credit facility [Member] | US Dollar Amounts [Member]
Long-Term Debt, by Current and Noncurrent, and Short-Term Debt
Short Term and Long Term Debt	328,000
Credit facility [Member] | Other Principal Trading Currencies [Member]
Long-Term Debt, by Current and Noncurrent, and Short-Term Debt
Short Term and Long Term Debt	16,858
Other local arrangements [Member]
Long-Term Debt, by Current and Noncurrent, and Short-Term Debt
Short Term and Long Term Debt	28,817
Other local arrangements [Member] | US Dollar Amounts [Member]
Long-Term Debt, by Current and Noncurrent, and Short-Term Debt
Short Term and Long Term Debt	0
Other local arrangements [Member] | Other Principal Trading Currencies [Member]
Long-Term Debt, by Current and Noncurrent, and Short-Term Debt
Short Term and Long Term Debt	$ 28,817